DEGRADATION OF BACILLUS-THURINGIENSIS DELTA-ENDOTOXIN IN HOST INSECT GUT JUICE

When Bacillus thuringiensis subsp. kurstaki HD-1 and subsp. sotto F-en dotoxins were activated from their protoxins in 50% Choristoneura fumi ferana gut juice, the amount of 60-65-kDa toxin protein produced was m uch less than that produced in 1% gut juice. In bioassays against Bomb yx mori larvae, the toxicity of activation mixtures with 50% C. fumife rana gut juice was less than activation mixtures with 1% gut juice. Di fferences between 50% and 1% B. mori gut juice in the amount of activa ted toxin produced from protoxin were much less pronounced. The presen t study may explain, in part, why B. thuringiensis subsp. kurstaki HD- 1 is more toxic to B. mori than to C.fumiferana larvae, and suggests t hat the enhancement of B. thuringiensis delta-endotoxin insecticidal a ctivity by protease inhibitors may be the result of reduced toxin degr adation in the insect midgut. (C) 1998 Federation of European Microbio logical Societies. Published by Elsevier Science B.V. All rights reser ved.